Update:
The menu styling issues sorted themselves out after a reboot.

So, if anyone else has CSS that is being ignored when you PREVIEW your work in progress in a browser, it might be worth trying either of these:

a) Close the program, wait a few moments and start a new session.
or
b) Close the program and close down your computer. A restart may get all the features working as expected.

Best wishes,

Daniel

I built the menu as per the video. I can find how the top level menu item triangle symbol is controlled so I can remove it. Similarly the borders on the vertical menu.

Thanks